Scientists' Contributions

Relatively high background ozone concentrations in Bulgaria

E. Donev

Department of Meteorology, Faculty of Physics, Sofia University, Bulgaria

    There are some data indicating that ground level ozone is a serious problem for southern Europe, and that concentrations are greater than in central and northern Europe. The climate in southern Europe is especially favorable for the formation ozone and high concentration episodes occurring often during the summer. In Bulgaria measurements of rural ground level O3 started in 1994 at the Ovnarsko climatology site - on the northwest slope of a high Rila mountain valley in the southwest part of Bulgaria. A second mountain site, Rojen, was initiated in October 1998 on the top of a gentle peak in the Rhodopa Mountain in the central south part of Bulgaria. In June 1999 the Ovnarsko site-monitoring equipment was moved to Ahtopol, a seacoast site in the southeast tip of Bulgaria close to the southern border with Turkey. All three sites are far from densely populated and industrial areas. Such parallel measurements of ozone concentrations are made for the first time in Bulgaria and the measurements will help to identify O₃ risk for Bulgarian forests in areas relatively far from industrial activities.

    The analysis of O₃ at three very different remote sites has demonstrated the impact of local geography and associated wind flows on concentrations. Compared to Rojen, the mountain top site (1700 m asl), the sea coast site, Ahtopol has over all lower concentrations and the mountain-valley site, Ovnarsko can have much higher one-hour concentrations. Rojen appears to be the best site for establishing background O3 concentration values for southern Bulgaria. That value is between 46 and 50 ppb for an overall background concentration. This value as well as the averages for the other two sites is higher than the AOT40 critical level for ozone. The results for the two five days periods 6-10 April and 24-28 August 99 are several times above from the critical level for causing visible damages. AOT60 values are also indicating a human health problem.